Carrier-board system for the production of oxygen-enriched gas streams and method for supplying the airways of the occupants of an aircraft

ABSTRACT

Apparatus and methods of supplying a highly enriched oxygen gas steam on board an aircraft. The gas stream is generated by an oxygen concentrator which concentrates atmospheric air by using at least one adsorber. The adsorber is made of a faujasite zeolite and has a Si/Al ratio between 1 and 1.5. The faujasite zeolite is also exchanged with silver by about 10%. Once generated, the gas stream is supplied to the airways of a person onboard an aircraft.

BACKGROUND

The present invention relates to systems and methods of generating anoxygen-enriched gas stream from atmospheric air for delivery to thepassengers and crew of an aircraft.

Oxygen concentrators on board aircraft, generally referred to by theacronym OBOGS, conventionally employ pressure swing adsorption (PSA orVPSA) processes that use adsorbents capable of separating theconstituents of air.

It is known to use for this purpose adsorbents of the zeolite X orzeolite A type that have a high affinity for nitrogen and are thereforecapable of delivering an oxygen-enriched mixture, but only up to acontent not exceeding, at best, 95% because of the argon content presentin the atmospheric air.

To deliver oxygen with a content greater than 95%, it has been proposed,for example in U.S. Pat. No. 4,566,881 (BWV), to use adsorbers incascade, in arrangements that are ill-suited for onboard applicationsowing to their size, weight and circuit complexity.

Moreover, zeolites exchanged with silver cations have been known for along time (cf. U.S. Pat. No. 3,331,190, Dow Chemical), which make itpossible in particular to improve the separation of oxygen from nitrogen(cf. WO-A-00/40332, University of Michigan) or to separate argon fromoxygen (cf. WO-A-94/06541, Arbor Research Corp.). However, there hasbeen no suggestion as to the possible use of such adsorbents in OBOGSconcentrators.

SUMMARY

The object of the present invention is to propose a method and anonboard system for generating a gas stream highly enriched with oxygen,which system is optimized in terms of onboard mass and onboard volumeand is suitable for various types of aircraft, in particular forlarge-capacity civil aircraft in order to deliver substantial volumes ofoxygen-enriched air to the occupants of the aircraft.

DESCRIPTION OF PREFERRED EMBODIMENTS

To do this, according to one feature of the invention, the onboardsystem for generating the oxygen-enriched gas stream from atmosphericair comprises at least one adsorber consisting of a faujasite zeolitehaving an Si/Al ratio between 1 and 1.5, advantageously between and 1and 1.25, and exchanged to at least 10% with silver, advantageouslybetween 20 and 60%, more particularly between 40 and 50%, with silverions, the zeolite, advantageously consisting of fine particles of lessthan 0.8 mm in size, being for example an NaX zeolite, a CaX zeolite orpreferably an LiX zeolite, advantageously an LiLSX zeolite exchanged toover 70% with lithium (lithium-exchanged zeolites, apart from theirexcellent performance in the separation of nitrogen, making it possibleto minimize the levels of exchange with silver ions, the latter having atendency, in the presence of lithium ions, to be fixed onto sites bettertargeted for the adsorption of argon), the degree of silver exchangethen being between 20 and 30%. Advantageously, the zeolite is an LiAgLSXzeolite such that the sum α+β, where α is the percentage of lithium andβ is the percentage of silver, is between 0.9 and 1.

The object of the invention is also to propose a method of generating ahighly oxygen-enriched gas mixture from atmospheric air employing atleast one system as defined below.

The system and the method according to the invention make it possible,under optimized operating conditions, to achieve oxygen concentrationsof greater than 98%, typically around 99%, or even close to 100%, whichtherefore makes it possible to ensure excellent compatibility with theoxygen distribution lines on current aircraft, which are designed foroxygen purities of 100% (bottled oxygen). In addition, such an oxygenconcentration level makes it possible to meet, without substantiallymodifying the operating conditions, the physiological requirement ofaircraft crew or passengers at high flight altitudes, in which theoxygen content in the surrounding air is low, for example in the case ofdecompression at an altitude of 40,000 feet (12,000 m) or, moregenerally, above 30,000 feet (10,000 m).

The system proposed within the context of the present invention istherefore, according to a preferred embodiment, an OBOGS system of theVPSA (Vacuum Pressure Swing Adsorption) type comprising at least onepair of adsorbers operating alternately, in a speedy fashion, typicallywith a cycle (pressurization/generation/regeneration-elution sequence)lasting less than 12 seconds, typically between 6 and 10 seconds. Withan LiAgLSX adsorbent having a mean particle size of less than 0.8 mm,preferably between 0.6 and 0.7 mm, exchanged to 80% with lithium and 20%with silver, for a civil airliner, typically carrying between 120 and500 passengers, the amount of sieve per adsorber is between 1.5 and 15kg, the high cycle pressure is between 500 millibar relative and 3 barrelative, and the low cycle pressure is correspondingly between 100millibar relative and 1 bar relative. Thus, a highly oxygen-enriched gasmixture, with an oxygen content exceeding 97%, can be generated,including at high altitudes, allowing considerable dilution with thecabin air, thus permitting substantial volumes to be produced, suitablefor a large number of passengers, even at high flight altitudes, theonboard VPSA system providing unlimited autonomy, allowing the aircraftto cruise at safety at high altitude, even in the event of a problemwith the air pressurization system.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

1. A method which may be used for supplying an oxygen enriched gasstream on an aircraft, said method comprising: a) generating a highlyenriched oxygen gas stream from atmospheric air with an oxygenconcentrator consisting essentially of at least one pair of adsorbers,wherein: 1) each of said adsorbers consists of a faujasite zeolite witha Si/Al ratio between about 1 and about 1.5; 2) said faujasite zeoliteis exchanged with silver to a degree between about 20% and 30%; 3) saidgas stream is generated by pressure swing adsorption; 4) the desorptionpressure is greater than about 0.100 bar relative; 5) the cycle time isless than about 10 seconds; 6) the oxygen content of said stream isgreater than about 98%; and b) supplying said oxygen gas stream to theairways of at least one person on an aircraft.
 2. The method of claim 1,wherein the air intake pressure is less than about 3 bar relative.
 3. Amethod which may be used for supplying an oxygen enriched gas stream onan aircraft, said method comprising: a) generating a highly enrichedoxygen gas stream from atmospheric air with an oxygen concentratorconsisting essentially of at least one pair of adsorbers, wherein: 1)each of said adsorbers consists of a faujasite zeolite with a Si/Alratio between about 1 and about 1.5; 2) said faujasite zeolite isexchanged with silver to a degree between about 20% and 30%; 3) said gasstream is generated by pressure swing adsorption; 4) said oxygenconcentrator has an air intake pressure less than about 3 bar relative;5) said oxygen concentrator has a desorption pressure greater than about0.100 bar relative; 6) said oxygen concentrator has a cycle time lessthan about 10 seconds; and 7) said gas stream has an oxygen contentgreater than about 98%; and b) supplying said oxygen gas stream to theairways of at least one person on an aircraft.
 4. The method of claim 3,wherein said zeolite is a NaX zeolite.
 5. The method of claim 3, whereinsaid zeolite is a LiX zeolite.
 6. The method of claim 5, wherein thedegree of exchange with lithium is greater than about 70%.
 7. A methodwhich may be used for supplying an oxygen enriched gas stream on anaircraft, said method comprising: a) generating a highly enriched oxygengas stream from atmospheric air with an oxygen concentrator consistingessentially of at least one pair of adsorbers, wherein: 1) each of saidadsorbers consists of a faujasite zeolite with a Si/Al ratio betweenabout 1 and about 1.5; 2) said faujasite zeolite is exchanged withsilver to a degree between about 20% and 30%; 3) said gas stream isgenerated by vacuum pressure swing adsorption, wherein the cycle time isless than about 10 seconds and the oxygen content of said stream isgreater than about 98%; b) supplying said oxygen gas stream to theairways of at least one person on an aircraft.
 8. The method of claim 7,wherein the desorption pressure is greater than about 0.100 barrelative.
 9. The method of claim 7, wherein the zeolite is an NaXzeolite.
 10. The method of claim 7, wherein the zeolite is an LiXzeolite.
 11. The method of claim 10, wherein the degree of exchange withlithium is greater than 70%.